B-Cell Lymphoma, Unclassifiable, with Features Intermediate Between Diffuse Large B-Cell Lymphoma and Burkitt Lymphoma

Abstract

This is a provisional category in the 2008 World Health Organization classification that includes aggressive lymphomas with histologic, biologic, and genetic features intermediate between diffuse large B-cell lymphoma (DLBCL) and Burkitt lymphoma (BL). Affected patients are mainly adults, presenting with nodal or extranodal disease, with frequent involvement of bone marrow, peripheral blood, and the central nervous system. The majority of cases are de novo, however some cases are the result of transformed follicular lymphoma. Most cases display a diffuse growth of intermediate- or occasional large-sized cells, high proliferation rate, admixed with few small reactive lymphocytes, and no stromal fibrosis. Frequent mitoses and a starry-sky pattern are common and reminiscent of BL. However, the cell variation is more distinct than usual BL and prominent nucleoli may occur. Rare cases composed of small cells with blastoid chromatin that mimics lymphoblastic lymphoma are also included in this category. In previous classifications, some cases that seemed like BL but with more nuclear variability were classified as atypical BL. However, gene profile studies of cases diagnosed with BL and atypical BL showed that they both share similar signatures, suggesting that they represent a spectrum of the same disease process. It became evident, therefore, that the category of atypical BL was unnecessary.